Bacteria may hold the key to figuring out how to tamp down our greenhouse gas problem. Researchers at Utah State University have been able to convert carbon dioxide emissions from fossil fuel combustion into usable fuels, according to a study published Monday in Proceedings of the National Academy of Sciences. Scientists used a phototropic bacterium — bacteria that respond to light stimuli — known as Rhodopseudomonas palustris as a catalyst to generate methane from the greenhouse gas.